You watch them next time they are together, and see.

They've been good friends for years." "Then all I can say is that some girls have a queer idea of friendship.
It's downright _catty_ the way they purr and rub around to your face, and then show their spiteful little claws when your back is turned.
That's what I've noticed Bernice doing lately.

She calls her all the sugary names in the dictionary when she's with her, but when her back is turned--well, it's just a shrug of the shoulders or a lift of the eyebrows or a little twist of the mouth maybe, but they insinuate volumes.

What makes girls do that way, Betty?
Boys don't.

If they have any grievance they fight it out and then let each other alone." "I'm sure I don't know why," answered Betty.